1. Field of the Invention
The present invention relates generally to rotary drill bits for drilling subterranean formations, and more specifically to retention of cutting element apparatuses for use with rotary drill bits for drilling subterranean formations.
2. State of the Art
Rotary drill bits employing polycrystalline diamond compact (“PDC”) cutters have been employed for drilling subterranean formations for a relatively long time. PDC cutters comprised of a diamond table formed under ultra high temperature, ultra high pressure conditions onto a substrate, typically of cemented tungsten carbide (WC), were introduced about twenty five years ago. As known in the art, drill bit bodies may comprise a so-called tungsten carbide matrix including tungsten carbide particles distributed within a binder material or may comprise steel. Tungsten carbide matrix drill bit bodies are typically fabricated by preparing a mold that embodies the inverse of the desired generally radially extending blades, cutting element sockets or pockets, junk slots, internal watercourses and passages for delivery of drilling fluid to the bit face, ridges, lands, and other external topographic features of the drill bit. Then, particulate tungsten carbide is placed into the mold and a binder material, such as a metal including copper and tin, is melted into the tungsten carbide particulate and solidified to form the drill bit body. Steel drill bit bodies are typically fabricated by machining a piece of steel to form generally radially extending blades, cutting element sockets or pockets, junk slots, internal watercourses and passages for delivery of drilling fluid to the bit face, ridges, lands, and other external topographic features of the drill bit. In both matrix-type and steel bodied drill bits, a threaded pin connection may be formed for securing the drill bit body to the drive shaft of a downhole motor or directly to drill collars at the distal end of a drill string rotated at the surface by a rotary table or top drive.
Conventional cutting element retention systems or structures that are currently employed generally comprise the following two styles: (1) tungsten carbide studs comprising a cylindrical tungsten carbide cylinder having a face oriented at an angle (back rake angle) with respect to the longitudinal axis of the cylinder, the face carrying a superabrasive cutting structure thereon, wherein the cylinder is press-fit into a recess that is generally oriented perpendicularly to the blades extending from the bit body on the bit face; and (2) brazed attachment of a generally cylindrical cutting element into a recess formed on the bit face, typically on a blade extending from the bit face. Accordingly, the first cutting element retention style is designed for a stud type cutting element, while the second cutting element retention style is designed for generally cylindrical cutting elements, such as PDC cutters. In either system, the goals are to provide sufficient cutting element attachment and retention as well as mechanical strength sufficient to withstand the forces experienced during the drilling operation. Of the two different types of cutting element retention configurations utilized in the manufacture of rotary drill bits, cylindrical cutting elements are generally more common. Stud-type cutting elements, on the other hand, are relatively uncommon and may require a brazing or infiltration cycle to affix the PDC or TSPs to the stud. Examples of other conventional cutting element attachment configurations include, inter alia, U.S. Pat. Nos. 6,283,234 to Torbet, 5,906,245 to Tibbitts, 5,558,170 to Thigpen et al., 4,782,903 to Strange, and 4,453,605 to Short.
Therefore, it would be advantageous to provide a cutting element retention configuration for use in rotary drill bits that ameliorates the disadvantages of conventional cutting element retention configurations. Further, it would be advantageous to provide a cutting element mechanism or apparatus that provides for ease of replacement or flexibility of design. Also, it may be advantageous to provide a cutting element retention mechanism and method that avoids directly brazing the cutting element to a drill bit.